1. Field of the Invention
The present invention relates to a novel drafting means for a fiber bundle. More specifically, it relates to a bottom tenser for tensioning an apron around a bottom roller of a high speed drafting means.
2. Description of the Prior Art
Recently, the processing speeds of spinning frames have been significantly increased. In fasciated yarn spinning, in which a fiber bundle attenuated by a drafting means is false-twisted in an air nozzle, processing speeds of 100 m/min, in some cases, 200 m/min, have been attained by actual machines.
Under such high processing speeds, however, more troubles occur in the drafting means compared to speeds of under 20 m/min, the maximum rate for conventional ring spinning frames. One of the most serious problems accompanying high speed drafting is damage of aprons wrapped around a middle roller for nipping the fiber bundle. In this regard, according to the present inventors' experience, most of the aprons provided on a high speed spinning frame wear out or break down after a one-month run. Therefore, it is essential to replace aprons periodically to ensure continuation of a normal spinning operation and, thus, good quality yarn.
As is well-known, however, it is very troublesome to replace aprons, particularly those wrapped around the bottom roller, in conventional spinning frames, due to the structure of the bottom roller. That is, the bottom roller is transversely disposed on the spinning frames along the row of all the spinning units arranged on one side of the spinning frame or along a row of, e.g., six or ten successive units. Provision of such a common bottom roller for a plurality of spinning units makes it unfeasible to replace individual aprons. Therefore, before individual apron wear becomes too severe, all the units common to the bottom roller are stopped and all the aprons common to the bottom roller are replaced. This, however, wastes both time and materials.
The present inventors have previously proposed an improved drafting means having one bottom roller for each one or two spinning units in Japanese Patent Application Nos. 57-92515 and 57-122374.
Though the exchanging operation of the apron is considerably improved by this novel drafting means, there are still some problems which prevent smooth exchange. One is due to the structure of the tenser.